1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) device and more particularly to an LCD device and a method for driving the same.
2. Discussion of the Related Art
Among various ultra-thin flat type display devices, which include devices having a display screen thickness several centimeters or less, liquid crystal display (LCD) devices are widely used for notebook computers, monitors, and spacecraft and aircraft displays because or their advantages such as low operating voltage, low power consumption, and portability.
A typical LCD device includes a lower substrate, an upper substrate, and a liquid crystal layer formed between the substrates.
Gate lines and data lines substantially perpendicular to the gate lines are formed on the lower substrate. The data lines and gate lines cross each other to define pixel regions. A thin film transistor (TFT) is formed at crossings of the gate lines and data lines.
Light shield layers are formed on the upper substrate to prevent leakage of light from regions corresponding to the gate lines, data lines, and TFTs. Color filter layers are also formed on the upper substrate between the adjacent light-shielding layers to transmit light of particular wavelengths.
The color filter layers add significantly to the manufacturing costs for a liquid crystal display device.
In order to solve this problem, an LCD device driven using a field sequential driving system has been developed.
FIG. 1 is a perspective view schematically illustrating a LCD device of the related art using a field sequential driving system.
As shown in FIG. 1, the LCD device of the related art includes a lower substrate 1, an upper substrate 2, and a liquid crystal layer (not shown) formed between the substrates 1 and 2.
Gate lines 10 and data lines 20 are formed on the lower substrate 1. The gate lines 10 and data lines 20 cross each other to define pixel regions 30. A TFT 41 functioning as a switching device is formed at each crossing of the gate lines 10 and data lines 20. A pixel electrode 35 is formed at each pixel region 30 and the pixel electrode 35 is connected to the TFT 41. A backlight unit 50 is arranged at a lower surface of the lower substrate 1, to irradiate light onto the lower substrate 1.
The backlight unit 50 includes a red light source 51, a green light source 52, and a blue light source 53.
A light shield layer 70 is formed on the upper substrate 2, in order to prevent leakage of light from regions where the gate lines 10, data lines 20, and TFTs 41 are arranged. A common electrode 80 is formed on the upper substrate 2 including the light shield layer 70.
In an LCD device using a field sequential driving method, no color filter is used in order to achieve an enhancement in the transmittance of light. To this end, the LCD device temporally reproduces color. That is, in the LCD device, various colors are displayed in a color reproduction period that is less than the temporal visual resolution to display a desired color.
By avoiding the forming of color filter layers in the LCD device, it is possible to save the costs of color filters and to achieve an improvement in color characteristics and image reproduction characteristics.
FIG. 2 is a timing diagram for explaining driving of the field sequential driving type LCD device of the related art shown in FIG. 1.
As shown in FIG. 2, in the field sequential driving type LCD device, one frame is time-divided into three sub-frames. A red (R) light source may be operated during the first sub-frame. During the second sub-frame a green (G) light source may be operated. During the third sub-frame a blue (B) light source may be operated.
In the field sequential driving type LCD device, the temporal period during which color is reproduced has a value less than the temporal visual resolution because one frame is sub-divided into three sub-frames. Accordingly, full color display may be achieved without using color filters.
In the first sub-frame, red (R) data is charged to a first pixel for a data charging time corresponding to a scan pulse from the gate line 10. After the response time of liquid crystal elapses the R light source is turned on.
In the second sub-frame the R light source is turned off and green (G) data is charged in a second pixel for a data charging time corresponding to a scan pulse from the gate line 10. After the response time of liquid crystal elapses the G light source is turned on.
In the third sub-frame the B light source is turned off and blue (B) data is charged in a third pixel for a data charging time corresponding to a scan pulse from the gate line 10. After the response time of liquid crystal elapses the B light source is turned on.
When the R light source is turned on, R light is emitted, so that an image according to the R light is displayed on a liquid crystal panel. Similarly, when the G or B light source is turned on, an image according to G or B light is displayed.
By sequentially turning on all the R, G, and B light sources during each frame, it is possible to display a desired color.
In the above-described sequential driving LCD device, however, each gate line is to be driven for a predetermined time within one frame period. Accordingly, as the number of gate lines is increased (for example to produce an LCD device of increased size) the time available for driving each gate line is shortened.
When the driving time for each gate line is shortened, the turn-on time of the TFTs connected to each gate line is shortened. As a result, for large sized LCD devices, there may be insufficient time to completely charge a data voltage into the pixels.
Although this problem may be at least partially addressed by increasing the size of the TFTs, there is a limitation in increasing the TFT size due to an associated design rule and problems associated with maintaining an aperture ratio.